1. Field of the Invention
The present invention relates to a transducer arrangement for controlling two relatively movable parts wherein the parts move a substantial distance apart during part of their cycle, but as they move together precise control is necessary, as for example in the control of a molding press.
2. Description of the Prior Art
Prior U.S. patent application Ser. No. 237,690, filed Feb. 24, 1981, now U.S. Pat. No. 4,470,787, issued Sept. 11, 1984 for Hydraulic Press shows an SMC Press which has a platen or press crosshead slidable along four columns and which crosshead carries an upper half of a mold. A bolster mounted on the press base or frame carries the lower half of the mold, and the crosshead is movable a substantial distance along the columns to permit opening the mold for service. However, when the mold parts move together it is necessary to precisely control their spacing by regulating the hydraulic cylinders that exert the molding pressure. In the form shown in said prior patent application, it is necessary to have two sets of transducers and some type of a mechanical or electric switch for transferring the control from transducers which control the position of the lower mold half with respect to the press base, to transducers which control the spacing of the mold halves relative to each other. This must be accomplished with a minimum of transient disturbances in the control, and must be done while the actuators are active.
Other transducer mounting arrangements have been made for providing different reference planes to reference the position of two relatively movable parts after a load has been applied to one of the parts, using telescoping members but with hydraulic reset. Such a device is shown in U.S. Pat. No. 3,839,944. However, automatic switching of the reference positions when the two parts move close to each other is not obtained.
The transducer described herein will provide the necessary control signals as set forth in prior U.S. Pat. No. 4,470,787, and the control arrangement for maintaining parallel relationships between the two mold parts, as well as controlling the molding forces, as described in said application.